The two principle attributes of the ideal internal combustion engine are high thermal efficiency and low emissions. In both four and two cycle engines, the presence of recycled exhaust gas in the combustion chamber interferes with the burning of the fuel-air mixture supplied to the chamber. The problem is particularly acute in two cycle engines at idle and light load.
Conventional engines are particularly low in efficiency at idle and light loads, and current attempts to reduce the emission of NO.sub.x, CO and HC tend to reduce the efficiency even lower than in unmodified engines. A basically poor combustion caused by burning fuel in combination with excessive amounts of recycled exhaust gas is the principle cause of both poor effiency and high emissions in conventional engines and it is an object of this invention to provide means whereby fuel is burned in truly stratified relation to recycled exhaust gas and to excess air. It will be shown that whereas two cycle engines in conventional form have been particularly handicapped by excessive emissions, principally of HC, they have, because of the large quantity of recycled exhaust gas inherent in their operation, been low in NO.sub.x emissions. It is an objective of this invention to retain this feature of two cycle engines while obtaining a fast, efficient and clean combustion under all operating conditions.